The plans submitted to the Environment Agency and the Department for Transport (DfT) include a road and rail tunnel across the River Thames that would incorporate a flood barrier, and a lagoon on the Kent side of the river where a tidal power plant would be built.
Consortium Metrotidal has worked up the plans for the £2bn to £4bn crossing from reclaimed land off Canvey Island in Essex up to Medway in Kent.
Under the £1bn tunnelling plan, worked up by consortium member Capita Symonds, the Thames would be dredged to form a trench into which 150m-long immersed concrete tubes would be placed to form the tunnel.
"This technique has been used successfully to construct the Oresund Link between Denmark and Sweden and the [existing] Medway Tunnel in very similar geological and tidal conditions," said Metrotidal director Mark Willingale.
Above the tunnel, a flood barrier would be built from Canvey Island to a newly formed lagoon off the Kent side of the estuary at Medway.
Four massive concrete caissons would be built to form a "throttle" for the flood barrier, greatly reducing the tidal range further upstream.
Under Metrotidal's plans, the flood barrier would be funded from the government's emerging flood defence budget. Finance for the tunnel and tidal power plant would come from road tolls for vehicles using the tunnel that would link the A13 and A130 with the M2, and tariffs paid by the rail operators.
The DfT has said it will study the need for a new crossing resulting from major port infrastructure planned at Shellhaven, which would greatly increase pressure on the existing road and rail system in the Thames Gateway.
Kent and Essex County Councils have already jointly launched a £100,000 feasibility study into a Lower Thames crossing.